Applications exist for an antenna for transmitting electrical signals wherein the antenna is preferably stored in a collapsed, compact configuration and released or extended to an operational state when desired. For example, such applications might include emergency locator beacons or communication satellites. Still another application involves sonobuoys. The latter are devices equipped with hydrophones for detecting underwater sounds and a radio for transmitting them via an appropriate antenna to a remote receiver. Large numbers of such sonobuoys, which in an actual operative environment, are comprised of cylindrical enclosures, may be launched by aircraft over the area to be monitored.
It is apparent that the space allotment in the shipping and launch containers carried by the aircraft is limited. At the same time, economy dictates that the largest number of sonobuoys be stored in such containers for subsequent deployment. Moreover, since the optimum length of the sonobuoy transmitting antenna is considerably greater than the longitudinal dimensions of the sonobuoy container, it is impractical to mount the antenna within the container. Likewise, the storage of sonobuoys with respective external antennas deployed for transmission such that the antenna axes are parallel to the longitudinal axes of the containers, is precluded by space limitations.
In addition to the advantage of using small sonobuoy containers to maximize the numbers of the latter which may be stored and launched at one time, another advantage unique to this application is realized. Reduction in the length of the sonobuoy container significantly reduces the total weight of the device. In free-fall situations, where deceleration means such as parachutes, are not utilized to provide cost savings, the impact velocity of the sonobuoy with the water is a function of its weight. Thus, the shorter container length reduces terminal impact velocity, thereby yielding improved impact survivability.
What is required to achieve the foregoing advantages is a collapsible external antenna of substantially optimum transmission efficiency, which may be stored within the envelope generated by the sonobuoy container, and which is readily erected when the sonobuoy is deployed in its operative environment. The antenna of the present invention fulfills all of the foregoing requirements and while it is admirably suited for the sonobuoy application, the invention should not be considered as limited thereto.